Designation D2370 − 16 Standard Test Method for Tensile Properties of Organic Coatings1 This standard is issued under the fixed designation D2370; the number immediately following the designation indi[.]
Designation: D2370 − 16 Standard Test Method for Tensile Properties of Organic Coatings1 This standard is issued under the fixed designation D2370; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision A number in parentheses indicates the year of last reapproval A superscript epsilon (´) indicates an editorial change since the last revision or reapproval This standard has been approved for use by agencies of the U.S Department of Defense 3.1.1 elongation at break, n—the increase in specimen length from the point of initial load application to the point of film rupture in a tension test 3.1.2 gage length, n—the initial length of the test specimen between the jaws of the tensile tester 3.1.3 stiffness (modulus of elasticity), n—the load per unit area required to elongate the film % from the first point in the stress-strain curve where the slope becomes constant 3.1.4 stress-strain curve, n—the curve resulting from a plot of tensile load against the distance of jaw separation (elongation of specimen) 3.1.5 tensile strength (nominal), n—the load per original unit area at which a specimen fails or yields in a tension (pull) test Scope 1.1 This test method covers the determination of the elongation, tensile strength, and stiffness (modulus of elasticity) of organic coatings when tested as free films 1.2 The values stated in SI units are to be regarded as standard The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use Referenced Documents Summary of Test Method 2.1 ASTM Standards:2 D823 Practices for Producing Films of Uniform Thickness of Paint, Varnish, and Related Products on Test Panels D882 Test Method for Tensile Properties of Thin Plastic Sheeting D1005 Test Method for Measurement of Dry-Film Thickness of Organic Coatings Using Micrometers D3980 Practice for Interlaboratory Testing of Paint and Related Materials (Withdrawn 1998)3 D4708 Practice for Preparation of Uniform Free Films of Organic Coatings 4.1 Free unsupported films of the materials to be tested are prepared in accordance with Test Method D4708 The tensile properties of the free films are determined by means of a tensile testing apparatus Significance and Use 5.1 Tensile properties determined by this method are of value in studying the behavior of coatings subjected to environmental stresses, such as those produced by aging and weathering (See Refs (1-10).)4 5.2 Tensile properties may vary with specimen thickness, method of preparation, gage length, rate of load application, tensile tester response, and type of grips used Consequently, where precise comparative results are desired, these factors must be carefully controlled Terminology 3.1 Definitions of Terms Specific to This Standard: This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of Subcommittee D01.23 on Physical Properties of Applied Paint Films Current edition approved July 1, 2016 Published November 2016 Originally approved in 1965 Last previous edition approved in 2010 as D2370 – 98 (2010) DOI: 10.1520/D2370-16 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website The last approved version of this historical standard is referenced on www.astm.org Apparatus 6.1 Equipment for applying films of uniform thickness as described in Practices D823 6.2 Micrometer Film Thickness Gage as described in Test Method D1005 Boldface numbers in parentheses refer to the list of references at the end of this standard Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959 United States D2370 − 16 facturer and models The material and method of making the marks must not affect the characteristics of the sample 6.3 Tensile Tester of the constant rate of jaw separation type, equipped with load cells having capacities of to 50 N (0.2 to 10 lb), and equipped with computer with tester controlling software, or optionally an indicating device such as an electronic constant speed chart recorder, a digital device that displays numerical values, or a printer that records the numerical values Tensile tester can also be equipped with a videoextensometer and environmental chamber, when higher accuracy of test is required and testing is conducted at an elevated or low temperature 10.3 Set the jaw separation of the tensile tester at the gage length selected Place the test specimen in the grips of the testing machine, taking care to align the long axis of the specimen with an imaginary line joining the points of attachment of the grips to the machine Tighten the grips evenly and firmly to the degree necessary to minimize slipping of the specimen during test NOTE 1—Mounting is facilitated by the use of air activated jaws Line-type jaws will minimize slippage and breakage The application of pressure-sensitive cloth to the ends of the film can improve jaw grip Special self-tightening grips designed to be used with thin films could also be used 6.4 Precision Specimen Cutter having a double blade with a foot to hold the sample in place5 or other suitable sharp cutter blade Test Specimens 10.4 Select a mutually agreed upon rate of elongation (strain rate) that is in the range of to 100 % ⁄min Set the crosshead speed of the tensile tester to provide this rate for the gage length chosen 7.1 The test specimens shall be free films having a width that is between 13 and 25 mm (1⁄2 and in.) No specimen shall vary by more than 62 % in width along its entire gage length The length shall be at least 50 mm (2 in.) longer than the gage length selected for the test NOTE 2—A rate of elongation should be selected that is optimum for testing the types of materials to be evaluated For relatively brittle films, elongation rates of to 20 % are suggested For relatively extensible films, elongation rates of 50 to 100 % are suggested (Refer to Test Methods D882 for relation of elongation rate to elongation at break) 7.2 Prepare free films by one of the procedures described in Test Method D4708 10.5 Elongate the test specimen until rupture of the film occurs and evaluate the stress-strain curve as follows: 10.5.1 Determine the specimen elongation from videoextensometer data or by measuring the increase in jaw separation from the point of original load application to the point of rupture 10.5.2 Measure the tensile pull in Newtons (lb) required to rupture the film 10.5.3 If stiffness is desired, determine the tensile stress in MPa to elongate the film % from the first point in the stress-strain curve where the slope becomes constant or allow the computer to calculate the appropriate tensile modulus Calibration 8.1 Balance, zero, and calibrate the load weighing and recording system of the tensile tester in accordance with methods specified by the manufacturer 8.2 If video-extensometer is used, calibrate instrument according to manufacturer’s instructions Conditioning 9.1 Specimens must be fully dried and cured before testing according to manufacturer specification Unless otherwise agreed upon between the producer and the user, condition the test specimens for at least 24 h at 23 2°C (73.5 3.5°F) and 50 % relative humidity and test in the same environment 10.6 Using the procedures in 10.1 – 10.5, run ten test specimens for each material under test 10 Procedure 11 Calculations 10.1 Select a mutually agreed upon gage length in the range of 25 to 125 mm (1 to in.) 11.1 Allow the computer software to calculate for each specimen elongation at break (EB), tensile strength at break (TS) and modulus of elasticity (if desired) from electronically stored test data points 10.2 Prepare 10 test specimens for each material to be evaluated These specimens should not exhibit any nicks or flaws and should be inspected under 10× magnification for the presence of potential defects Measure the thickness of each specimen to 60.1 µm (0.04 mil) with a micrometer in accordance with Test Methods D1005, taking five measurements within the gage length area If a video-extensometer is used, apply markings on the sample within the distance of gage length selected The markings on the sample must be readable by the instrument being used These will vary between manu- 11.2 If a manually operated tensile tester is used, for each specimen compute the following: 11.2.1 The elongation at break EB, in percent from the following equation: EB E 100 S D ∆L L (1) where: ∆L = increase in specimen length to break, and L = initial specimen length (gage length) The sole source of supply of the JDC precision cutter known to the committee at this time is the Thwing-Albert Instrument Co., 10960 Dutton Rd., Philadelphia, PA 19154 If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters Your comments will receive careful consideration at a meeting of the responsible technical committee,1 which you may attend 11.2.2 The tensile strength, TS, in MPa (lb per sq inch), from the equation: TS ~ P R ! / ~ TW! (2) D2370 − 16 12.3.1 Tensile strength, 12.3.2 Elongation, and 12.3.3 Stiffness (modulus of elasticity), if desired where: PR = tensile pull to rupture, N (lb), T = thickness of test specimen, m (in.), and W = width of test specimen, m (in.) 12.4 Report the conditions of the test 12.4.1 Procedure for preparation of free films, 12.4.2 Rate of elongation in percent per minute, 12.4.3 Specimens gage length and grip separation speed 12.4.4 Temperature and relative humidity during test, and 12.4.5 Aging and treatment given the specimens 11.2.3 The stiffness (modulus of elasticity), S, from the following equation: S ~ P E ! / ~ TW! (3) where: PE = pull in Newtons (lb) to elongate the film % from the first point in the stress-strain curve where the slope remains constant, T = thickness of test specimen, m (in.), and W = width of test specimen, m (in.) 13 Precision and Bias 13.1 Precision—An interlaboratory test of this test method was conducted in which three coatings (representing a brittle film, a film with limited elasticity, and a very elastic film) were tested by five laboratories The test was conducted with Instron tensile testers operated at two elongation rates (10 and 100 %) with a specimen gage length of 50 mm (2 in.) and specimen thicknesses of 65 to 90 micrometers (2.5 to 3.5 mils) The between laboratory coefficients of variation were found to be 30 % for percent elongation and 18 % for tensile strength Based on these coefficients, the following criteria should be used for judging the acceptability of results at the 95 % confidence level: 13.1.1 Reproducibility—Two results for percent elongation obtained by operators in different laboratories should be considered suspect if they differ by more than 118 % of their mean Two results for tensile strength obtained by operators in different laboratories should be suspect if they differ by more than 70 % of their mean 11.3 Examine the uniformity of the tensile strength and elongation results obtained for the ten specimens measured for a material Choose one of the following procedures for discarding spurious values and calculate the mean of the remaining results: 11.3.1 Use the results from those five specimens showing the highest tensile strength in evaluating all three properties, discarding those from the remaining five This is done on the basis that the expected errors (nicks or flaws in the specimen, breaks within the jaw, slippage in the jaw, etc.) would all tend to produce results on the low side 11.3.2 Discard the values for those specimens where both the tensile strength and elongation values are significantly lower than those for most of the specimens Use the test for outliers given in Practice D3980 – 88 12 Report 12.1 Type and manufacturer of the tensile tester and extensometer, as well as the software that controls the instrument 13.2 Bias—Since there is no accepted reference material suitable for determining the bias for the procedure in this test method for measuring tensile properties using tensile testers, bias has not been determined 12.2 Produce stress-strain curves for all tested specimens (if instrumentation used allows) 14 Keywords 12.3 Report the mean average dimensions: thickness and width of each specimen and values obtained with the test specimens for: 14.1 elongation; organic coatings; stiffness; tensile properties; tensile strength REFERENCES (1) Ashton, H E., “Flexibility and Its Retention in Clear Coatings Exposed to Weathering,” Journal of Coatings Technology, Vol 51, No 653, June 1979, pp 41–52 (2) Ashton, H E., “Predicting Durability of Clear Finishes for Wood from Basic Properties,” Journal of Coatings Technology, Vol 52, No 663, April 1980, pp 63–71 (3) Beardsley, Herbert P., and Kennedy, Richard J., “Performance of Exterior Paints Based on a Vinyl Acetate-Ethylene Emulsion Vehicle,” Journal of Paint Technology, Vol 39, No 505, February 1967, pp 88–98 (4) Evans, Robert M., and Fogel, Joseph, “Comparison of Tensile and Morphological Properties With Abrasion Resistance of Urethane Films,” Journal of Coatings Technology, Vol 49, No 634, November 1977, pp 50–60 (5) Holsworth, Richard M., Provder, Theodore, and Ranig, Alexander, Jr., “Physical Characterization of Coatings Upon Aging,” Journal of Paint Technology, Vol 46, No 596, September 1974, pp 76–95 (6) Levine, Eli, Lindlaw, William, and Vona, Joseph A., “Some Recent Developments in Water-Based Systems,” Journal of Paint Technology, Vol 41, No 537, October 1969, pp 531–536 (7) Pierce, Percy E., and Holsworth, Richard M., “The Mechanical Properties and Performance of Wood Primers,” Journal of Paint Technology, Vol 38, No 501, October 1966, pp 584–590 (8) Shur, E G., and Rubin, H., “Accelerated Testing of Finishes For Hardboard,” Journal of Paint Technology, Vol 41, No 537, October 1969, pp 537–550 (9) Schurr, Garmond G., Hay, T Kirk, and Van Loo, Maurice, “Possibility of Predicting Exterior Durability by Stress/Strain Measurements,” D2370 − 16 Journal of Paint Technology, Vol 38, No 501, October 1966, pp 591–599 (10) Yaseen, M., and Ashton H E., “Effect of Free Film Preparation Method on Organic Coatings,” Journal of Coatings Technology, Vol 49, No 629, June 1977, pp 50–58 ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM International Headquarters Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards, at the address shown below This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above address or at 610-832-9585 (phone), 610-832-9555 (fax), or service@astm.org (e-mail); 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